A dust cover has been used in a conventional ball joint provided in various kinds of equipment in a vehicle or the like in order to prevent water or dust from coming into a joint part and prevent grease from flowing out from the joint part. With reference to FIGS. 4 and 5, an exemplary conventional dust cover will be described. FIG. 4 is a schematic sectional view of the exemplary conventional dust cover. FIG. 5 is a partly enlarged sectional view of the exemplary conventional dust cover (a sectional view showing a sealing part thereof in an enlarged state).
The ball joint includes a ball stud having a spherical part at an end of a shaft part thereof and a socket that supports the ball stud in a rotatable and swingable manner. The ball stud is attached to a knuckle or the like provided at a vehicle body.
A dust cover 800 includes a deformable film-like body part 810, a fixed part 820 provided on one end side of the body part 810 and fixed to the socket, and a sealing part 830 provided on the other end side of the body part 810. Here, the sealing part 830 includes an inner peripheral sealing part 831 which is swingably provided at the shaft part of the ball stud and a dust lip part 832 which is provided slidably relative to the knuckle. In the illustrated conventional example, an annular groove 834 to which a snap ring is mounted is provided on an outer peripheral surface of the dust cover at a portion where the sealing part 830 is provided. Therefore, an annular protrusion 835 that protrudes radially outward is formed between an end surface of the sealing part 830 on the other end side and the annular groove 834.
In recent years, as the ball joint has been reduced in size, an area of a surface with which the dust lip part 832 comes into close contact (such as an end surface of the knuckle) may be reduced. The dust lip part 832 is shortened to cope with the reduction. However, it is difficult to keep the shortened dust lip part 832 in close contact with the knuckle in a stable manner. The dust lip part 832 deforms to be curved in the direction indicated by the arrow R in FIG. 5 to come into close contact with the knuckle, and the shortened dust lip part 832 has a greater curvature, which may cause stress to concentrate on the base part of the dust lip part 832. This lowers the durability. In particular, in a configuration in which the annular protrusion 835 must be provided at an end of the sealing part 830 on the other end side as in the illustrated conventional example, the outer peripheral surface of the dust lip part 832 is shortened, and the above described disadvantage becomes more significant.